Weight loss is often prescribed as the initial treatment for obese patients with noninsulin dependent diabetes mellitus (Type 2 diabetes). While high blood sugar levels are reduced by this treatment, they often increase again after treatment due to regaining of weight. In addition, even in those patients who are successful in keeping weight off, blood sugars often increase despite their diligence. Therefore, the overall objectives include: 1) designating the mechanisms by which glucose homeostasis is regulated; 2) determining why hyperglycemia is exacerbated after weight loss even when maintaining reduced-obese weight; and 3) identifying how the clinical and metabolic efficacy of weight management can be enhanced in this patient population. The procedures to be used are: hyperinsulinemic euglycemic clamp and oral glucose clamp (0G-clamp). During 12 weeks of weight loss, the two treatment groups will be given liquid nutritional supplements to help eliminate food choices that may result in weight regain. Some patients will receive supplements that are higher in monounsaturated fatty acids, a diet component that has been shown to lower blood sugar, while others will receive a high carbohydrate, low fat supplement. The weight maintenance phase will last 3 months with patients receiving individualized mixed meals, in addition to their nutritional supplements. Clinical and metabolic testing will be performed at baseline and every 3 months to determine the patients' responses to these therapies.